[Python-3000] How far to go with cleaning up exceptions (original) (raw)

Collin Winter collinw at gmail.com
Sat Mar 3 01:39:51 CET 2007

On 3/1/07, Brett Cannon <brett at python.org> wrote:

I spent my sprint time cleaning up exceptions for Py3K and Guido suggested I run some things by the group to make sure they don't make transitioning from 2.6 too difficult. After adding the proper restrictions in terms of what can and cannot be raised or caught, I began cleaning up BaseException's API per PEP 352.

First thing I did was remove slicing. That wasn't too bad since I just got exceptions about the lack of getitem and went to the affected line and tossed in '.args' between the index and the exception. Not sure if 2to3 can handle this as it would need to realize when an exception is within scope and then insert '.args' when it is be indexed on.

2to3 currently cannot handle this. 2.6's "py3k-compat" mode could handle it easily, though.

The next thing I did was strip out the use of '.args' and make BaseException take a single argument that gets assigned to 'message'. The fruits of this labour are in the p3yknoargsonexc branch. This one turned out to be a pain in the rear. [snip]

I took at stab at this same conversion a few weeks ago and had the exact same experience. I ended up resolving my frustration by applying "svn revert" and working on something else : )

I think this will shape up to be one of the harder parts of porting from 2.x to 3.0.

As for transforming the 'args' accesses to something else, I guess 2to3 could automatically do 'args[0]' accesses to 'message', but anything else will need to be changed by hand.

There's very little 2to3 can do on this front. I think 2.6's py3k-compat flag is going to be the best bet for this particular conversion.

Collin Winter

More information about the Python-3000 mailing list